1. Field of the Invention
The present invention relates to an ultrasonic sensor that includes a sending device and a receiving device separately.
2. Description of the Related Art
Conventionally, an ultrasonic sensor provided in a vehicle includes a sending device and a receiving device separately. The ultrasonic sensor sends an ultrasonic wave from the sending device, and the ultrasonic wave reflected by an external object is received by the receiving device. Thereby, the ultrasonic sensor detects a direction of the object and a distance to the object. An environment surrounding a vehicle is monitored by using the ultrasonic sensor for enabling a safety drive. For example, the ultrasonic sensor is used for an automatic-parking support system. In the present case, a back sonar including the ultrasonic sensor is disposed at a rear portion of the vehicle. The back sonar detects an ultrasonic wave reflected by people or an obstacle behind the vehicle by using the ultrasonic sensor, and thereby the vehicle can be backed in a parking space without colliding with the people or the obstacle. As an example of the ultrasonic sensor used for a vehicle, JP-2006-234523A discloses an ultrasonic sensor that includes a sending device and a plurality of receiving devices that are arranged to face in the same direction.
The sending device sends the ultrasonic wave into a sending area and the receiving device receives the ultrasonic wave from a receiving area. Thus, in order to detect an obstacle by using the above-described ultrasonic sensor, the obstacle is required to be both in the sending area and the receiving area. That is, the above-described ultrasonic sensor can detect only an obstacle that is located in an overlapping area of the sending area and the receiving area. Thus, when a distance between the ultrasonic sensor and the obstacle is shorter than a distance between the ultrasonic sensor and overlapping area, the ultrasonic sensor cannot detect the obstacle.